Abstract
Endemic species are believed to converge on narrow ranges of traits, with rarity reflecting adaptation to specific environmental regimes. We hypothesized that endemism is characterized by limited trait variability and environmental tolerances in two Dianthus species (Dianthus pseudocrinitus and Dianthus polylepis) endemic to the montane steppes of northeastern Iran. We measured leaf functional traits and calculated Grime’s competitor/stress-tolerator/ruderal (CSR) adaptive strategies for these and co-occurring species in seventy-five 25-m2 quadrats at 15 sites, also measuring a range of edaphic, climatic, and topographic parameters. While plant communities converged on the stress-tolerator strategy, D. pseudocrinitus exhibited functional divergence from S- to R-selected (C:S:R = 12.0:7.2:80.8% to 6.8:82.3:10.9%). Canonical correspondence analysis, in concert with Pearson’s correlation coefficients, suggested the strongest associations with elevation, annual temperature, precipitation seasonality, and soil fertility. Indeed, variance (s2) in R- and S-values for D. pseudocrinitus at two sites was exceptionally high, refuting the hypothesis of rarity via specialization. Rarity, in this case, is probably related to recent speciation by polyploidy (neoendemism) and dispersal limitation. Dianthus polylepis, in contrast, converged towards stress-tolerance. ‘Endemism’ is not synonymous with ‘incapable’, and polyploid neoendemics promise to be particularly responsive to conservation.
Highlights
Endemic species are believed to converge on narrow ranges of traits, with rarity reflecting adaptation to specific environmental regimes
We focused on how functional traits and CSR strategies of these two contrasting endemic Dianthus species vary in range and character in their respective habitats and with respect to other, non-endemic, sympatric species
A clear dominance of relatively stresstolerant strategies was evident across the sites; most species showed a proportion of S exceeding 50%
Summary
Endemic species are believed to converge on narrow ranges of traits, with rarity reflecting adaptation to specific environmental regimes. While plant communities converged on the stress-tolerator strategy, D. pseudocrinitus exhibited functional divergence from S- to R-selected (C:S:R = 12.0:7.2:80.8% to 6.8:82.3:10.9%). Narrow endemics occupy distinct habitats, often associated with restricted ranges of environmental conditions[1,2], or small overall geographic ranges This association, and that between environmental parameters and traits that affect survival[3], suggests that endemics are rare owing to adaptive specialization and selection in favor of limited ranges of trait values and functioning (i.e. evolutionary convergence). While local environmental conditions may select for species exhibiting a convergent subset of potential trait values, finer-scale divergence within the plant community (i.e. local dissimilarity or variance in trait values) is expected as a result of adaptation to micro-scale environmental regimes (i.e. niche differentiation)[4]. We expect (1) general functional convergence within the community, but (2) functional divergence between the endemic species and non-endemic sympatric species, and (3) relatively restricted trait variances for the endemics
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